Budget airline Ryanair has called for "immediate" EU action to prevent a summer of travel chaos after it revealed more than 1,100 flights were cancelled last month due to air traffic control strikes, impacting over 200,000 customers.

The Dublin-based carrier said the flight cancellations were caused largely by the strike action in France and air traffic control (ATC) staff shortages, although it added that disruption from widespread thunderstorms last month were also partly to blame.

But despite the May strike woes, Ryanair's latest passenger traffic figures show a 6% increase in passenger numbers last month to 12.5 million.

Its load factor - a measure of how well airlines fill their planes - improved to 96% from 95% a year earlier.

The latest strike disruption comes after Ryanair's flight cancellation debacle last September, when more than 700,000 customers were impacted after it was forced to scrap flights over mismanaging pilots' annual leave.